From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 401CC143C6C for ; Tue, 7 May 2024 08:31:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715070717; cv=none; b=V+TVKIPZvocIt11Uay0qqTLenyF9fmkgglcXX7Hkv1wNOcDeIH0Ad17OgYkuMY8HAoKj3ivE26vABNjNFhlp6QOU19em8DSv+htDrMakpSmKrG3i5jIcfpvi5LeB/OYK7WPaDf7WrlmPzYN123WWD2/0XXECD1yg1IAXxK5EYX8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715070717; c=relaxed/simple; bh=rxjgmTJY356gbfLe+hoAimBuO98HddJcAQLBx5Oylc0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rG5iUmPLniM2YduPb6WY5vMuYinyGJFPjXwE8TXHYx8BxS8GEYoQ5xLVzVMn9zbliWqhtvAd6dVKBAYtDoeO6TeSinLZUBZ7gkE9SeiaC8qera+D22Mxm8LONV4aQCsyg2TmOfp6xBHihv4ay3aJFydRTXkkOU7K3BRht9S3CJQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 81869106F; Tue, 7 May 2024 01:32:18 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC0D53F793; Tue, 7 May 2024 01:31:49 -0700 (PDT) Date: Tue, 7 May 2024 10:31:40 +0200 From: Beata Michalska To: Viresh Kumar Cc: Vanshidhar Konda , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ionela.voinescu@arm.com, sudeep.holla@arm.com, will@kernel.org, catalin.marinas@arm.com, vincent.guittot@linaro.org, sumitg@nvidia.com, yang@os.amperecomputing.com, lihuisong@huawei.com Subject: Re: [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq Message-ID: References: <20240405133319.859813-1-beata.michalska@arm.com> <20240405133319.859813-5-beata.michalska@arm.com> <76zutrz47zs6i2cquvjo2qn7myxpq7e3c6alhper7n3wrkhf5h@22l5t5pio2cd> <20240429092515.2ehk4ifcul6mbaxh@vireshk-i7> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240429092515.2ehk4ifcul6mbaxh@vireshk-i7> On Mon, Apr 29, 2024 at 02:55:15PM +0530, Viresh Kumar wrote: > On 26-04-24, 12:45, Beata Michalska wrote: > > It seems that we might need to revisit the discussion we've had around > > scaling_cur_freq and cpuinfo_cur_freq and the use of arch_freq_get_on_cpu. > > As Vanshi has raised, having both utilizing arch specific feedback for > > getting current frequency is bit problematic and might be confusing at best. > > As arch_freq_get_on_cpu is already used by show_scaling_cur_freq there are not > > many options we are left with, if we want to kee all archs aligned: > > we can either try to rework show_scaling_cur_freq and it's use of > > arch_freq_get_on_cpu, and move it to cpuinfo_cur_freq, which would align with > > relevant docs, though that will not work for x86, or we keep it only there and > > skip updating cpuinfo_cur_freq, going against the guidelines. Other options, > > purely theoretical, would involve making arch_freq_get_on_cpu aware of type of > > the info requested (hw vs sw) or adding yet another arch-specific implementation, > > and those are not really appealing alternatives to say at least. > > What's your opinion on this one ? > > Hi Beata / Vanshidhar, > > Lets forget for once what X86 and ARM may have done and think about it > once again. I also had a chat with Vincent today about this. > > The documentation says it clearly, cpuinfo_cur_freq is the one > received from hardware and scaling_cur_freq is the one requested from > software. > > Now, I know that X86 has made both of them quite similar and I > suggested to make them all aligned (and never received a reply on my > previous message). > > There are few reasons why it may be worth keeping the definition (and > behavior) of the sysfs files as is, at least for ARM: > - First is that the documentation says so. > - There is no point providing the same information via both the > interfaces, there are two interfaces here for a reason. > - There maybe tools around which depend on the documented behavior. > - From userspace, currently there is only one way to know the exact > frequency that the cpufreq governors have requested from a platform, > i.e. the value from scaling_cur_freq. If we make it similar to > cpuinfo_cur_freq, then userspace will never know about the requested > frequency and the eventual one and if they are same or different. > > Lets keep the behavior as is and update only cpuinfo_cur_freq with > arch_freq_get_on_cpu(). > > Makes sense ? > First of all - apologies for late reply. It all makes sense, though to clarify things up, for my own benefit, and to avoid any potential confusion .... Adding arch_freq_get_on_cpu to cpuinfo_cur_freq does seem to be the right approach - no argue on this one. Doing that though means we need a way to skip calling arch_freq_get_on_cpu() from show_scaling_cur_freq(), to avoid having both providing the same information when that should not be the case. In the initial approach [1], that was handled by checking whether the cpufreq driver supports 'get' callback (and thus cpuinfo_cur_freq). In case it didn't, things remained unchanged for scaling_cur_freq. That does not seem to be a viable option though, as there are at least few drivers, that will support both: cpuinfo_cur_freq alongside scaling_cur_freq (+ APERF/MPERF) and for those, we would hit the initial problem of both relying on arch_freq_get_on_cpu. So I guess we need another way of avoiding calling arch_freq_get_on_cpu for show_scaling_cur_freq (and most probably avoid calling that one for cpuinfo_cur_freq). Quick idea on how to not bring arch specificity into cpufreq generic code would be to introduce a new flag for cpufreq drivers though that seems a bit stretched. Will ponder a bit about that but in the meantime suggestions are more than welcomed. Aside: I will most probably send the changes separately from this series to not mix things any further. --- [1] https://lore.kernel.org/all/20230606155754.245998-1-beata.michalska@arm.com/ --- BR Beata > -- > viresh